Northeastern Guangxi Research Articles

Episodic Nb–Ta mineralisation in South China: Constraints from in situ LA–ICP–MS columbite-tantalite U–Pb dating

South China hosts many Nb–Ta deposits that show evidence for episodic mineralization, which were generated during the emplacement of composite granites. To constrain the spatio-temporal distribution of Nb–Ta mineralisation in the region and to identify future targets for mineral exploration, we used in situ laser ablation-inductively coupled plasma-mass spectroscopy to date 23 columbite-tantalite group mineral (CGM) samples from 14 Nb–Ta deposits. Our CGM U–Pb data, supplemented by previous results, reveal five distinct Nb–Ta mineralisation events in South China as follows: (1) Late Silurian–Middle Devonian (ca. 424–391 Ma; e.g., the Xigang and Nanping deposits in eastern Jiangxi and western Fujian Provinces); (2) Triassic (ca. 248–204 Ma; e.g., the Houxi, Cunxin, Dongtounan, Shenkeng, Limu and Gaoling deposits in western Guangdong Province and northeastern Guangxi Zhuang Autonomous Region; (3) Late Jurassic (ca. 160–150 Ma; e.g., the Gedongping, Yichun, Laiziling, Jianfengling and Jinzhulong deposits in Guangxi, Jiangxi and Hunan Provinces); (4) Early Cretaceous (ca. 130 Ma; e.g., the Huangshan and Songshugang deposits in northeastern Jiangxi province); and (5) Late Cretaceous (ca. 90 Ma; e.g., the Jiepailing deposit, located along the boundary between Hunan and Jiangxi Provinces). We show that Nb–Ta mineralisation in South China was controlled by multiple tectono-magmatic events. Our CGM samples yielded Caledonian (ca. 424–391 Ma), early Indosinian (ca. 248 Ma) and late Yanshanian (ca. 130 Ma) ages, indicating that Nb–Ta mineralisation was abundant during these times and should form the focus for future studies of mineralisation in the region. Early Triassic granite in the Guangning Nb–Ta metallogenic district in western Guangdong Province, Indosinian and early Yanshannian granites in the Miao’ershan–Yuechengling batholith in northeastern Guangxi, and the Late Cretaceous Lingshan batholith in northern Jiangxi Province are identified as targets for future Nb–Ta exploration.

Spiradiclis quanzhouensis sp. nov. (Rubiaceae) from a limestone area in Guangxi, China

Spiradiclis quanzhouensis, a new species of Rubiaceae from northeastern Guangxi, China is described and illustrated. It is similar to S. umbelliformis, but can be distinguished by its rosulate habit, subglabrous stems, leaf blades that are pubescent on both surfaces, lanceolate purple‐pubescent stipules that are undivided or sometimes bifid in apical 1/3, an inflorescence with 2–4 flowers, lanceolate 4–5 mm long calyx lobes that are purple‐pubescent outside, a salveriform corolla that is light purple‐pubescent outside, a semi‐inferior ovary, and capsules that are light purple‐pubescent with persistent calyx lobes 5–6 mm, in fruit 2 × as long as capsule.

Oreocharis crispata, a new species of Oreocharis (Gesneriaceae) from Guangxi, China

Oreocharis crispata, a new species of Oreocharis (Gesneriaceae) from northeastern Guangxi, China, is described and illustrated. The new species is compared with its most morphologically similar species O. nemoralis and O. magnidens. Besides, the relationship between the new species and Oreocharis × heterandra is discussed here.

New precise zircon U-Pb and muscovite 40Ar-39Ar geochronology of the Late Cretaceous W-Sn mineralization in the Shanhu orefield, South China

The Shanhu orefield, located in the northeastern Guangxi province, is an important part of W-Sn polymetallic metallogeny in the Nanling region. The Shanhu W-Sn deposit is spatially associated with the Yantianling granite. LA-ICPMS zircon U-Pb dating of the Yantianling granite yields Late Cretaceous ages of 100.9±2.2Ma and 100.8±2.3Ma. Hydrothermal muscovite 40Ar/39Ar dating yields plateau ages of 102.7±1.7Ma and 100.8±0.7Ma. This date coincides well with the LA-ICPMS zircon U-Pb age of the Yantianling granite, indicating a spatial-temporal link between the W-Sn mineralization and the granitic magmatism. In combination with regional geological data, it is suggested that a Late Cretaceous mineralization event related to granitic magmatism occurred in the Nanling region, which might have resulted from regional lithospheric extension.

Oreocharis curvituba, a new species of Gesneriaceae from northeastern Guangxi, China

Oreocharis curvituba, a new species of Gesneriaceae from Guangxi, China, is described and illustrated. It resembles O. stenosiphon and O. magnidens in the leaf characters, but it differs from the latter by its corolla with tube slightly curved, marked with purple star and a ring of glandular hairs at mouth.

The Silurian A‐Type Granites in Northeastern Guangxi, South China Block: New Evidence of Transition from Compression to Post‐orogenic Extension of the Kwangsian Orogen

Acta Geologica Sinica - English EditionVolume 90, Issue 5 p. 1913-1914 Research Advances The Silurian A-Type Granites in Northeastern Guangxi, South China Block: New Evidence of Transition from Compression to Post-orogenic Extension of the Kwangsian Orogen Xiaohui JIA, Corresponding Author Xiaohui JIA jxh1226@126.com Wuhan Center of Geological Survey, China Geological Survey, Wuhan 430223, Hubei, ChinaCorresponding author. E-mail: jxh1226@126.comSearch for more papers by this authorXiaodi WANG, Xiaodi WANG Wuhan Center of Geological Survey, China Geological Survey, Wuhan 430223, Hubei, ChinaSearch for more papers by this authorGongjian TANG, Gongjian TANG State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, Guangdong, ChinaSearch for more papers by this authorWenqiang YANG, Wenqiang YANG Wuhan Center of Geological Survey, China Geological Survey, Wuhan 430223, Hubei, ChinaSearch for more papers by this authorZhijun NIU, Zhijun NIU Wuhan Center of Geological Survey, China Geological Survey, Wuhan 430223, Hubei, ChinaSearch for more papers by this author Xiaohui JIA, Corresponding Author Xiaohui JIA jxh1226@126.com Wuhan Center of Geological Survey, China Geological Survey, Wuhan 430223, Hubei, ChinaCorresponding author. E-mail: jxh1226@126.comSearch for more papers by this authorXiaodi WANG, Xiaodi WANG Wuhan Center of Geological Survey, China Geological Survey, Wuhan 430223, Hubei, ChinaSearch for more papers by this authorGongjian TANG, Gongjian TANG State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, Guangdong, ChinaSearch for more papers by this authorWenqiang YANG, Wenqiang YANG Wuhan Center of Geological Survey, China Geological Survey, Wuhan 430223, Hubei, ChinaSearch for more papers by this authorZhijun NIU, Zhijun NIU Wuhan Center of Geological Survey, China Geological Survey, Wuhan 430223, Hubei, ChinaSearch for more papers by this author First published: 16 November 2016 https://doi.org/10.1111/1755-6724.12829Citations: 3AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article.Citing Literature Volume90, Issue5October 2016Pages 1913-1914 RelatedInformation

Upper Devonian reefs and microbialite at Maoying, South China—implications for paleoenvironmental changes

Reefal carbonate deposits in South China preserve a record of community structure and environmental change across the Frasnian-Famennian boundary and through the Late Devonian, detailing a regional response to one of the largest mass extinction events in Earth history. The Upper Devonian (Frasnian to Famennian) limestone outcrops in the Maoying area of northern Ziyun County, South China, record a carbonate platform depositional setting with some patch reef development. The Upper Devonian carbonate deposits in Maoying area are distinctive from those in correlative sections in Dushan County with rare argillaceous limestone and dolomitic limestone as well as less dolostone. Exposures to the south in the Guilin area of northeastern Guangxi Province are similar to those seen in the study area. Upper Devonian carbonates in the Maoying area are divided into two lithologic groups, reef limestones or dolostone beds, composed of five lithologically distinctive intervals. The Upper Devonian strata have a cumulative thickness of 530m. The Upper Devonian reefs in the Maoying area were developed on a shell pavement of brachiopod- and bivalve-shell shoal packstones and evolved into patch reefs in the interior of the carbonate platform. Patch-reef development was limited to early Frasnian time. Reef-building organisms are dominated by massive and tabular stromatoporoids, Amphipora sp., Stachyodes sp., and coral Thamnopora sp., while brachiopods and algae accumulated between stromatoporoid skeletal frameworks. Three evolutionary stages of the Frasnian patch reefs, including an initial development stage, maturity stage and demise stage, can be recognized according to sedimentary structures and fossil assemblage characteristics. The Frasnian strata overlying the patch reefs represent a well-bedded back-reef depositional setting and are mainly composed of Amphipora floatstone and packstone containing a few bulbous stromatoporoids and small fasciculate corals. Famennian strata are characterized by laminated limestone and fenestrate limestone that are interbedded with infrequent mudstone and argillaceous limestone horizons. A prominent microbialite bed developed in the laminated limestone of the Famennian carbonate platform consists of stromatolite and thrombolite framestone. This bed can be correlated, in horizon and age, with microbial reefs and mounds in the Famennian offshore carbonate platform in the Huanan Epeiric Sea (such as Famennian microbial reefs and mounds in Guilin). This represents a biogenic carbonate formation characterized by microbial fabrics that accumulated in a nearshore carbonate platform setting after the global Frasnian/Famennian biotic extinction event, which promoted the growth of microbialites during the latest Devonian in South China.

A new species of the genus Pachytriton (Caudata: Salamandridae)from Hunan and Guangxi, southeastern China.

Despite recent descriptions of multiple new species of the genus Pachytriton (Salamandridae), species richness in this China-endemic newts genus likely remains underestimated. In this study, we describe a new species of Pachytriton from northeastern Guangxi and southern Hunan, southeastern China. Both molecular analyses and morphological characters reveal that the new species can be distinguished from its congeners. The mitochondrial gene tree identified the new lineage highly divergent (uncorrected p-distance > 5.8 % by mitochondrial gene) from currently recognized species and placed it as the sister species of P. xanthospilos and P. changi. Furthermore, a nuclear gene haplotype network revealed a unique haplotype in the new populations. Statistical species delimitation using Bayes factor strongly supported the evolutionary independence of the new species from the closely-related P. xanthospilos. Morphologically, the new species is characterized by a uniformly dark brown dorsum without bright orange dots or black spots; irregular orange blotches on the venter; tips of fingers and toes orange on the dorsal side; moderately developed webs on the side of digits; absence of costal grooves between the axilla and groin; and widely open vomerine tooth series.

First cavernicolous trechine beetle discovered in Guilin karst, northeastern Guangxi (Coleoptera, Carabidae, Trechinae).

A new subgenus and new species of anophthalmic trechine beetles, Oodinotrechus (Pingleotrechus) yinae subgen. n., sp. n., is described and illustrated from a limestone cave called Chaotianyan in southern part of Guilin karst, northeastern Guangxi Zhuang Autonomous Region. The new taxon is very different from the Maolan-Mulun congeners belonging to the nominate subgenus Oodinotrechus (s. str.) Uéno, 1998, in several important character states including pronotal structure, elytral chaetotaxy and male genitalia. It is the first record of a cavernicolous trechine beetle in Guilin karst, and in the eastern part of Guangxi. In addition, a distribution map for the genus Oodinotrechus Uéno, 1998, is provided.

Aspidistra lingchuanensis (Asparagaceae), a new species from Guangxi, China

The genus Aspidistra Ker-Gawler (1822: 628) (Asparagaceae) has its main centre of diversity in China and Vietnam. In recent years, many new species were discovered and described from that region, increasing the total number of species to over 120. In China, Aspidistra includes over 80 species and is mainly distributed in the southwest part of the country, especially in Guangxi Zhuang Autonomous Region (60 species) (Liang & Tamura 2000, Li 2004, Tillich 2005, 2008, Liu et al. 2011, Tillich et al. 2013, He et al. 2013, Lin et al. 2013a–b, 2014, Meng et al. 2014). When investigating medicinal plants in Qingshitan Natural Reserve, Lantian town, Lingchuan County, northeastern Guangxi in 2013, we collected an unusual Aspidistra specimen with linear leaves and urceolar perigone. In March 2014, we returned to the place for further observations of the species, the plant flowered regularly. After consulting herbarium specimens and relevant literature on Aspidistra, it became apparent that we had a new species at hand.

Radar observations of the seasonal migration of brown planthopper (Nilaparvata lugens Stål) in Southern China.

The summer and autumn migrations of the brown planthopper (Nilaparvata lugens) were observed in Southern China with a millimetric scanning entomological radar and a searchlight trap supplemented with capture in field cages, field surveys, and dissections of females. Nilaparvata lugens took off at dusk and dawn in summer, but in autumn there was sometimes only a dusk take-off. The variation of the area density of the radar targets indicated that flight durations were about 9-10h. In summer, planthopper-size targets generally flew below 1800m above ground level (AGL), although some insects reached 2000m AGL; in autumn, they flew lower, generally below 1100m although some insects reached 1700m AGL. Multiple layer concentrations were seen every night in both summer and autumn. The depths of these layers in autumn were less than in summer. Nilaparvata lugens flew in strong winds; wind shear may be the main factor causing them to accumulate and form dense layers at certain heights. Nilaparvata lugens emigrating in summer from the vicinity of the radar site in the Northeastern Guangxi Zhuang Autonomous Region, and carried by the prevailing southwesterly wind, would have travelled northeastwards and reached Northern Hunan Province. In autumn, with the prevailing northeasterly wind, emigrants would have reached overwintering areas (south of 21°N).

桂东北稻区第七代褐飞虱迁飞规律及虫源分析

褐飞虱是我国水稻上的一种重要迁飞性害虫，在桂东北稻区不能越冬。近年来，作为次害代的第7代褐飞虱在桂东北稻区频繁暴发，桂东北稻区作为褐飞虱南北往返迁飞的重要通道，研究阐明该稻区第7代褐飞虱的迁飞规律及虫源分布，对第7代褐飞虱的早期预警和有效防控意义重大。利用灯光诱捕的方法研究了2007-2010年桂东北稻区褐飞虱的迁飞动态，并运用大气质点轨迹分析平台HYSPLIT（Hybrid Single-Particle Lagrangian Integrated Trajectory）和气象图形处理软件GrADS（Grid Analysis and Display System）对褐飞虱迁入、迁出峰次进行轨迹分析和气象背景分析。结果表明：（1）桂东北稻区第7代褐飞虱每年都会出现2-3次迁飞高峰，虫量高峰期主要集中在9月底至10月上旬。（2）迁入虫源主要来自江西中西部和湖南中东部稻区，从本地起飞的部分褐飞虱飞行24 h或36 h后能到达广西南部沿海、越南北部和海南等越冬区。（3）925 hPa的温度高则褐飞虱虫量高；盛行东北气流较多的年份，褐飞虱发生严重；微弱的下沉气流和无雨天气有利于褐飞虱的迁飞。;Brown planthopper (BPH), <em>Nilaparvata lugens</em>(Stål), is one of the most important migratory rice pests in China. The northeast of Guangxi Zhuang Autonomous Region, which is not an overwintering area for BPH, is situated in a double-cropping rice region and is near the Xiang-gui Corridor, the major pathway for the seasonal northward and return migration of BPH in China. In recent years, infestations of the 7^th generation of BPH, which is regarded as a secondary devastating generation, have frequently broken out in this region, leading to higher production costs and a serious loss of rice yield for farmers. The migration of BPH to China in spring has increased with the increased backward migration of BPH towards the Indo-China Peninsula during the previous autumn. However, research on the migratory patterns of the 7^th generation of BPH is seldom reported. An investigation into the migrating and source areas of this generation has been initiated as a first step towards developing procedures for forecasting and suppressing significant infestations of BPH. Our studies were conducted between 2007 and 2010 in Xing'an county, northeastern Guangxi Zhuang Autonomous Region, with a view to providing reference data for the forecasting and control of BPH. A Jiaduo light trap and a searchlight trap were used to monitor the migratory periods of BPH. The migration process of BPH and the atmospheric conditions during those periods were analyzed with HYSPLIT, a trajectory analysis system, to simulate the migration trajectories of migratory BPH, and also with GrADS software. From this, we ascertained the migration rule of the 7^th generation of BPH and their source areas. Furthermore, the relationship between migration of BPH and atmospheric conditions was examined.<br>There were two or three peak migratory periods for the 7^th generation of BPH every year, which generally occurred between late September and early October, in northeastern Guangxi Zhuang Autonomous Region. There are significant differences in immigratory periods, emigratory periods and migratory amount for different years. Most of the immigrant BPH in Xing'an county apparently originated in the mid-west of Jiangxi Province and the mid-east of Hunan Province. Nevertheless, the emigrant BPH from Xing'an county would land mainly in the central part of Guangxi Zhuang Autonomous Region if they flew for 12 h. After 24 h or 36 h of flight, they would land in the south of Guangxi Zhuang Autonomous Region, the north of Vietnam, and on Hainan island which were overwintering areas for BPH. They mainly flew in warm air at about 925 hPa pressure. Our earlier study demonstrated that the critical temperature for flight was a daily average of 20℃. A northeasterly airflow at the 925 hPa pressure level was the major impetus for the return migration of the 7^th generation of BPH. They tended to migrate when it was not raining and there was a weak pressure drop. In conclusion, the searchlight trap can trap BPH effectively in any migratory period, so when combined with the Jiaduo light trap, it can help determine the migratory characteristics of BPH. We suggest that plant protection stations use the searchlight trap to monitor and control BPH.

Timing of hydrothermal activity associated with the Douzhashan uranium-bearing granite and its significance for uranium mineralization in northeastern Guangxi, China

The Miaoershan uranium (U) ore field in northeastern Guangxi is one of the important granite-related U deposits in south China and is closely related to the Douzhashan U-bearing granite. The Douzhashan granite contains primary U-rich accessory minerals, including monazite (UO2 = 0.98–1.75 wt%) and xenotime (UO2 = 1.48–6.14 wt%). Primary monazite and xenotime yield chemical ages of 231 ± 28 Ma and 230 ± 38 Ma by electron microprobe analysis and U-Pb isotopic ages of 220±6 Ma and 211±7 Ma by laser ablation-inductively coupled-mass spectrometry respectively. These ages demonstrate that the Douzhashan granite formed during the period of Indosinian magmatic activity. Back scattered electron imaging shows that monazite and xenotime are commonly altered to assemblages of low-U synchisite and apatite, which was associated with loss of U to hydrothermal fluids. U-Th-Pb analyses of secondary apatite yielded a chemical age of 136 ± 17 Ma, which corresponds to the timing of Cretaceous-Tertiary crustal extension in south China. We suggest that the heat and CO2 required for mineralization was the result of Yanshanian crustal extension, and that this triggered the breakdown of U-rich accessory minerals in the Douzhashan U-bearing granite. Uranium remobilization from the Douzhashan granite provided materials for mineralization within the granite and/or surrounding country rocks. Therefore, a combination of Indosinian compression and Yanshanian extensional overprint produced the hydrothermal U deposits associated with the Douzhashan granite.

Indosinian isotope ages of plutons and deposits in southwestern Miaoershan-Yuechengling, northeastern Guangxi and implications on Indosinian mineralization in South China

The Miaoershan-Yuechengling complex pluton is the largest granitoid complex in the western Nanling metallogenic belt with a surface exposure of >3000 km2. The complex pluton is composed of an early stage granitoid batholith and late stage small intrusions. The early stage batholith contains mainly medium-grained porphyritic mica granite and porphyritic monzonite granite, whereas the late stage intrusions are composed of muscovite granite porphyry and muscovite monzonitic granite. There are many W-Sn-Mo-Pb-Zn-Cu ores in the contact zone between the batholith and strata, forming an ore-rich belt around the batholith. Based on zircon LA-ICP-MS U-Pb ages, the southwestern part of the early stage batholith formed at 228.7 ± 4.1 Ma (MSWD = 2.49), with slightly earlier magmatic activity at 243.0 ± 5.8 Ma (MSWD = 2.62). The Yuntoujie muscovite granite was associated with W-Mo mineralization and has a zircon LA-ICP-MS U-Pb age of 216.8 ± 4.9 Ma (MSWD = 1.44). The Re-Os isochron age of molybdenite from the Yuntoujie W-Mo ore was 216.8 ± 7.5 Ma (MSWD = 11.3). Our new isotope data suggest that the late stage intrusive stocks from the southwestern Miaoershan-Yuechengling batholith were closely associated with W-Mo mineralization from the Indosinian period. These new results together with previous isotope data, suggest that South China underwent not only the well-known Yanshanian mineralization event, but also a widespread Indosinian metallogenic event during the Mesozoic period. Therefore, South China has a greater potential for Indosinian mineralization than previously thought such that more attention should be given to the Indosinian ore prospecting in South China.

Two New Species of Pachytriton from Anhui and Guangxi, China (Amphibia: Urodela: Salamandridae)

Abstract: Two new species of the salamandrid genus Pachytriton are described from Anlui and Guangxi, China, based on molecular and morphological analyses. One of them from Huangshan, Anhui, has smaller body, longer limbs, and larger eye than the remaining congeners. The other from northeastern Guangxi possesses a larger body and head, and longer snout and tooth series than the remaining congeners. Also, we have found that two individuals of Pachytriton obtained from pet shops in Japan can represent an unnamed species, but do not describe them as new because we have no exact information on their original localities. The distribution patterns and ecological relationships among species of Pachytriton are discussed.

Two New Species of Pachytriton from Anhui and Guangxi, China (Amphibia: Urodela: Salamandridae)

Two new species of the salamandrid genus Pachytriton are described from Anhui and Guangxi, China, based on molecular and morphological analyses. One of them from Huangshan, Anhui, has smaller body, longer limbs, and larger eye than the remaining congeners. The other from northeastern Guangxi possesses a larger body and head, and longer snout and tooth series than the remaining congeners. Also, we have found that two individuals of Pachytriton obtained from pet shops in Japan can represent an unnamed species, but do not describe them as new because we have no exact information on their original localities. The distribution patterns and ecological relationships among species of Pachytriton are discussed.

Molybdenite Re‐Os and Zircon SHRIMP U‐Pb Dating at the Baishiding Deposit, Guposhan District: New Evidence for Silurian Mo Mineralization in South China

AbstractThe Baishiding molybdenum deposit is located in the Central‐Middle Guangxi depression zone of the South China Caledonian fold zone. Orebodies occur as quartz‐molybdenite veins within the Guiling monzonite pluton and arkosic quartz sandstone of Zhengyuanling Group in the northeastern Guangxi. They are NEE‐trending with a dip angle of 75–80°. Zircon SHRIMP U‐Pb geochronologic analyses of the Guiling monzonite show age of 424.4 ± 5.6 Ma. It indicates that the Guiling monzonite was emplaced in Silurian. The ore minerals in quartz‐molybdenite veins contain molybdenite, pyrite, chalcopyrite and scheelite. Six molybdenite samples yield Re‐Os ages between 433.3 ± 6.3 Ma and 417.2 ± 5.7 Ma, with a weighted mean age of 424.6 ± 5.7 Ma, which agrees with the zircon age of the Guiling monzonite pluton. It suggests that the deposit was formed in the Silurian, not the Jurassic as previously thought. The Baishiding deposit is the only Silurian molybdenum deposit so far recognized in the South China. It was probably formed in a crustal shortening setting along the continental margin in the Silurian.

Hf isotopic composition of zircons from the Huashan-Guposhan intrusive complex and their mafic enclaves in northeastern Guangxi: Implication for petrogenesis

High precision zircon U-Pb dating indicates that main intrusive bodies (Tong’an, Niumiao, Huashan, Lisong), and a mafic microgranular enclave in the Huashan-Guposhan complex were formed at 160–163 Ma. The ɛHf(t) values of zircons from the Huashan granite vary from −2.8 to +0.3 and those from the Lisong granite vary from −2.3 to +0.3, which are obviously different with those values (+2.6 to +7.4) of the mafic enclaves from the Lisong granite. These Hf isotopic data indicate that the mafic enclaves and host granites were crystallized from different sources of magmas, providing evidence for mafic-felsic magma mixing processes. The highest ɛHf(t) value of zircons from the mafic enclaves is up to +7.4, indicating that the mafic magma was originated from a relatively depleted mantle source. Studies on regional geology and the contemporaneous mafic and alkaline rocks in this area indicate that the mafic magma was not originated from reworking of basaltic juvenile crust, but from partial melting of the mantle. However, it remains to be resolved whether the mafic magma was derived from partial melting of the asthenosphere or the lithospheric mantle. The Huashan granite and the Lisong granite were formed from hybrid magma of mantle-derived and crust-derived magmas, and the mafic enclaves are considered as remains of mantle-derived magma during mixing processes. The ɛHf(t) values of zircons from the Niumiao diorite vary from −1.1 to +2.1, and those from the Tong’an quartz monzonite vary from −1.7 to +1.7. These values are lower than those from the mafic enclaves, suggesting that the diorite and monzonite were formed from different source-derived magma with the mafic enclaves. The ɛHf(t) values for the Niumiao diorite and the Tong’an monzonite are only slightly higher than those for the Hushan granite and the Lisong granite. Abundant mafic enclaves also occur in the Niumiao diorite and in the Tong’an monzonite. Thus, we suggest that the Niumiao diorite and the Tong’an monzonite were probably also formed from the same hybrid magma as the granites but come through less degree of fractional crystallization and crustal contamination. The strong mantle-derived and crust-derived magma mixing caused by an intense crustal extension and thinning in the Mid-Late Jurassic may be the major mechanism for generating the diorites and granites in southeastern Hunan and northeastern Guangxi belt in South China.

05/00569 Geochemistry of oil in fluid inclusions in a middle Proterozoic igneous intrusion: implications for the source of hydrocarbons in crystalline rocks

Reefal carbonate deposits in South China preserve a record of community structure and environmental change across the Frasnian-Famennian boundary and through the Late Devonian, detailing a regional response to one of the largest mass extinction events in Earth history. The Upper Devonian (Frasnian to Famennian) limestone outcrops in the Maoying area of northern Ziyun County, South China, record a carbonate platform depositional setting with some patch reef development. The Upper Devonian carbonate deposits in Maoying area are distinctive from those in correlative sections in Dushan County with rare argillaceous limestone and dolomitic limestone as well as less dolostone. Exposures to the south in the Guilin area of northeastern Guangxi Province are similar to those seen in the study area. Upper Devonian carbonates in the Maoying area are divided into two lithologic groups, reef limestones or dolostone beds, composed of five lithologically distinctive intervals. The Upper Devonian strata have a cumulative thickness of 530 m. The Upper Devonian reefs in the Maoying area were developed on a shell pavement of brachiopod- and bivalve-shell shoal packstones and evolved into patch reefs in the interior of the carbonate platform. Patch-reef development was limited to early Frasnian time. Reef-building organisms are dominated by massive and tabular stromatoporoids, Amphipora sp., Stachyodes sp., and coral Thamnopora sp., while brachiopods and algae accumulated between stromatoporoid skeletal frameworks. Three evolutionary stages of the Frasnian patch reefs, including an initial development stage, maturity stage and demise stage, can be recognized according to sedimentary structures and fossil assemblage characteristics. The Frasnian strata overlying the patch reefs represent a well-bedded back-reef depositional setting and are mainly composed of Amphipora floatstone and packstone containing a few bulbous stromatoporoids and small fasciculate corals. Famennian strata are characterized by laminated limestone and fenestrate limestone that are interbedded with infrequent mudstone and argillaceous limestone horizons. A prominent microbialite bed developed in the laminated limestone of the Famennian carbonate platform consists of stromatolite and thrombolite framestone. This bed can be correlated, in horizon and age, with microbial reefs and mounds in the Famennian offshore carbonate platform in the Huanan Epeiric Sea (such as Famennian microbial reefs and mounds in Guilin). This represents a biogenic carbonate formation characterized by microbial fabrics that accumulated in a nearshore carbonate platform setting after the global Frasnian/Famennian biotic extinction event, which promoted the growth of microbialites during the latest Devonian in South China.